Controls the ratio of velocities after a collision (coefficient of restitution). This attribute is used by the Simulate Rigid
Bodies node to calculate particle motion.
When two bodies collide, the elasticity of the interaction is the product of the elasticities of the two bodies. The elasticity
of obstacles is set in the Simulate Rigid Bodies node.
In a head-on collision at a value of 1.0, the velocities stay the same as before the collision but with opposite directions.
At a value of 0.0, colliding particles stick to each other and share the same velocity after the collision. Values above 1
mean that that particles increase their energy each time they collide.
If this attribute is undefined, the default value used by the Simulate Rigid Bodies node is 0.5.
Note that energy and momentum cannot be transferred to an obstacle object or passive rigid body particle; they can only be
transferred between two colliding non-passive particles.